Acoustic alarm device

ABSTRACT

A loudspeaker is adapted to be energized by an alternating current signal to provide an audible output signal of progressively increasing intensity. An alarm controlled switch applies the signal to a loudspeaker. The increase in intensity of the audible signal is facilitated by a thermistor connected in series with the loudspeaker. A high-pass filter and rectifier circuit in series with the thermistor enhance the production of harmonics of the signal frequency thereby to provide an improved audio tone and to permit said tone, or alarm signal, to be readily heard over a broad intensity range. A vibrator attached to the speaker provides a second audible signal after a predetermined audio intensity is achieved.

United States Patent [72] Inventor John W. Chaliant 8325 S.W. 86thTerrace, Miami, Fla. 33143 [21] Appl. No. 853,295

[22] Filed Aug. 27, 1969 [45] Patented Dec. 28, 1971 [54] ACOUSTIC ALARMDEVICE [56] 7 References Cited UNITED STATES PATENTS 2,517,368 8/1950Wiseley 58/19 34; .SwiiclL Primary Examiner-Richard B. Wilkinson 7Assistant Examiner-Lawrence R. Franklin Attorney-Lloyd J. AndresABSTRACT: A loudspeaker is adapted to be energized by an alternatingcurrent signal to provide an audible output signal of progressivelyincreasing intensity. An alarm controlled switch applies the signal to aloudspeaker. The increase in intensity of the audible signal isfacilitated by a thermistor connected in series with the loudspeaker; Ahigh-pass filter and rectifier circuit in series with the thermistorenhance the production of harmonics of the signal frequency thereby toprovide an improved audio tone and to permit said tone, or alarm signal,to be readily heard over a broad intensity range. A vibrator attached tothe speaker provides a second audible signal after a predetermined audiointensity is achieved.

Patented Dec. 28, 1971 3,631,450

Switch 1? 10, COIL'ZTOL 14] l I? Power ;7 gi gg Harmonic Dual, .50 12Network Generajor Transducer switch H CorbiroL q Bu 1" "3 5 INVENTOB 8JOIUL WClla lfani BY v 4 Time A TTOBNE Y8 ACOUSTIC ALARM DEVICEBACKGROUND OF THE INVENTION The types of alarm clocks for variouspurposes available on the market today are legion. They are availablewith buzzers, chimes, radios, flashing lights and many other variedaudible visual, and/or physical alarm mechanisms, of which many have theobjective of awakening the sleeper. Most. of these alarmclocks provide acontinuous audible output level usually of sufficient intensity toawaken even the deepest sleeper. Unfortunately, this high intensity orloud alarrn signal, even though in some cases it may be varied inintensity, by an adjustment knob or lever, does not meet the needs ofmany people. Depending upon the sleepers state of fatigue and relatedfactors, varying intensity sounds may be required to arouse him. Statedsimply, the sleepers threshold of sensitivity varies with his physicalcondition. Hence, too loud an alarm is often used providing in efi'ect anerve shattering output even though in most cases such high-intensityaudio signal is not necessary. In order to avoid the shock anddiscomfort of aloud signal the sleeper has the option of obtaining analarm with a muffled or low-level sound or of manually setting the alarmintensity control to a lower volume level. In either case, he must takea chance that the low-level signal is not too low to awaken him. Ifunwilling to assume such a calculated risk, the sleeper will oftentolerate too loud an alarm system with the attendant shock to hisnervous system.

One US. Pat. No. 2,856,751 issued Oct. 21, I958 to Ralph H. Preiserattempts to obviate these difficulties by providing what is termed anAutomatic Crescendo Alarm. The Preiser alarm utilizes a thermistor inseries with abell such that the bell initially emits a relativelylow-intensity sound but as the thermistor warms up due to the solenoidcurrent passing therethrough, the bell emits a sound of increasingintensity. Hence, even though Preiser has taken a step towardeliminating the objection to most of the presently available alarmclocks, the Preiser audible signal is still a relatively harsh tone and,due to the inherent limitations of most solenoid bells, the dynamicaudible range provided by the bell is limited, with a relatively highinitial or minimum noise level.

Accordingly, it is an object of this invention to provide an improvedacoustic alarm device which produces an audible signal having arelatively pleasant tone.

Another object of this invention is to provide an improved acousticalarm device which produces an audible output signal of high intensityand having a relatively large dynamic range.

A further object of the invention is the provision of a dynamicloudspeaker in which the voice coil thereof is adapted to move in anoscillatory amplitude sufficient to cyclic impact against a rigid memberfor producing audible shock waveemission from the diaphragm of theloudspeaker.

BRIEF DESCRIPTION OF THE INVENTION In a preferred embodiment of thisinvention an alarm device is constructed to have a sound transducingmeans, a switch means for applying-a low-frequency alternating currentvoltage signal to the sound transducing means thereby to produce anaudible oscillating signal varying in content and intensity with thefrequency and amplitude of the voltage signal applied thereto, animpedancemeans coupled in circuit with the transducing means and theswitch means for increasing the amplitude of the voltage signal that isapplied to the transducing means as a function of time. Finally,harmonic generating means are coupled in circuit with the transducingmeans for generating harmonics of the voltage signal for application tothe transducer, thereby improving the quality of the audible alannsignal, and the ease with which it, together with correspondingintensity changes, may be heard.

In one form of vthe invention, a vibrator or member arm is attached tothe loudspeaker so that the axial movement of the voice coil interactswith the end of the vibrator arm to cause impact vibration thereof. Thisadditional vibrationproduces a simultaneous audible signal in the coreor diaphragm of the loudspeaker to provide an output signal of increasedaudio intensity and increased dynamic frequency range.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features that are consideredcharacteristics of this invention are set forth with particularity inthe appended claims. The invention, itself, however, both as to itsapparatus and method as well as additional objects and advantagesthereof, will best be understood from the following description whenread in connection with the accompanying drawings, in which:

FIG. 1 is a block diagram of an acoustic alarm system constructed inaccordance with this invention;

FIG. 2 is a schematic circuit diagram of an acoustic alarm deviceconstructed in accordance with a preferred embodiment of this invention;

FIG. 3 is an enlarged partial sectional view of a loudspeakerillustrating the preferred manner in which the vibrator arm is attachedthereto;

FIG. 4 is an enlarged partial cross-sectional view of the speaker coneillustrating an alternative manner in which the vibrator arm may beattached to the loudspeaker; and

FIG. 5 is a graphical illustration of the alarm devices response inwhich the sound intensity produced by the vibrator arm and loudspeakeris plotted as the ordinant and time is plotted as the abscissa.

A may be a conventional source of line voltage, is connected through aswitch 12 to an amplitude control network illustrated by the block 14thence to a harmonic generator illustrated by the block 16 to energize adual transducer denoted by the block 18. The switch 12 may be actuatedby a switch control device denoted by the block 34. The switch controldevice in practice may be a conventional clock mechanism or some othertype of actuator (electrical or mechanical) controlled as by the openingof a door or the passage of a person past a photocell, etc. In itspreferred embodiment, the form of the switch control device 34 is aclock mechanism which operates through a suitable mechanical linkagedenoted by the dashed line 36 to close the switch 12.

The amplitude control network 14 may include a thermistor or othercircuit element having a negative temperature coefficient of resistanceso that the electrical signal allowed to pass therethrough progressivelyand gradually increases in amplitude as a function of time as thecircuit element, in this case a thermistor, begins to heat up andthereby its resistance value decreases. Alternatively, other timingcircuits such as those with an RC voltage level control of current flowor other timing circuits both electrical and mechanical which control orvary current flow as a function of time may be used.

The signal after passage through the amplitude control network 14 thenpasses to a harmonic generator 16 whose function is to modify thehannonic content of the voltage signal passing therethrough as byclipping or similar known techniques. By increasing the harmonic contentof this signal, which is then applied to the dual transducer 18, aricher, more pleasing audible tone results. The dual transducer 18, mayin a preferred embodiment of this-invention, comprise a conventionalminiature permanent magnet dynamic loudspeaker. In alternativeembodiments any type of sound transducer may be used. This electricalsignal having a high harmonic content, is reproduced by the transducerto provide the audible alarm signal which increases in intensity withtime.

The specific circuit details of one system that has been successfullybuilt and operated are shown in the schematic drawing of FIG. 2. Thus,the power source 10, which in this instance is illustrated by theconventional generator symbol, provides an alternating 60 Hertz (Hz.)voltage signal such as that derived from a normal wall outlet of mosthouses. The voltage signal is connected through a step down transformer11 so as to provide a lower voltage. This reduced voltage signal fromthe transformer 11 is passed through the switch 12, actuated by thelinkage 36 from the switch control device 34, as described, to athermistor 38. A unidirectional conducting device, such as a diode 40,and a capacitor 42 are connected in series between the thermistor 38 andone end of the voice coil of a loudspeaker 44. in turn the other end ofthe voice coil 43 is returned to the transformer 11 to complete thiscircuit. The diode 40 has a variable resistor 50 connected in parallel.The capacitor 42 may be a conventional low voltage, high-capacityelement such as is provided by an electrolytic capacitor. A neon lamp 26or other indicator may be connected in the load circuit to indicate whenpower is on, i.e., when the switch 12 is closed.

With the circuit arrangement shown, it may be assumed that the switchcontrol device 34 operates through the linkage 36 to close the switch12. With the closing of the switch 12, the low-voltage alternatingcurrent signal from the step down transformer 11 energizes the neon lamp26 indicating the alarm is on and passes a current through thethermistor 38. The initial high resistance of the thermistor 38 limitsthe current to a relatively low value. This current signal in turn hasits negative going excursions clipped by the diode 40. The variableresistor 50 is maintained at a relatively high-resistance level tocontrol the degree of clipping. if its value is reduced, the clipping isdecreased. In any event, this low current, clipped signal is passedthrough the capacitor 42 which is selected to have a value that presentsa relatively high impedance to the fundamental 60 Hertz frequencycomponent but yet presents a significantly lower impedance to thepassage of higher frequency components. This has the effect ofamplifying" the higher frequency components with respect to the 60 Hz.fundamental frequency component. The clipping function performed by thediode 40 causes the generation, predicted according to Fourier analysis,of plural odd harmonics of the fundamental frequency. These oddharmonics freely pass-through the capacitor 42, to the voice coil 43 ofthe loudspeaker 44 while the fundamental component is attenuated. Thus,the initial audible signal produced by the loudspeaker 44 is one oflow-audio intensity complete with many harmonics of the fundamentalfrequency thereby producing a more pleasing tone to the car than isnormally available from the pure 60 Hertz hum.

As the thermistor 38 begins to heat with the current passingtherethrough its resistance decreases such that the speaker 44 producesan audible signal of progressively increasing intensity. This operationis illustrated in the graphical representation of FIG. in which theaudio output signal produced by the speaker is illustrated by the line60. It may be noted that at zero time (the time the switch control 34closed the switch 12,) the output signal sound intensity is relativelylow. This intensity progressively increases until the maximum isreached, this maximum being represented either by the maximum signalapplied from the source or from the point at which the speaker becomesoverloaded and does not produce a greater intensity signal. This maximumintensity point is represented by the upper portion of the line 60designated by the numeral 92.

In accordance with a preferred embodiment of this invention a smallloudspeaker 44 is provided, as may be seen most clearly in FIG. 3, witha rigid or substantially rigid vibrator arm 62-. ln the illustration ofFIG. 3, the speaker itself is illustrated as having a cone portion 64,the voice coil 66, which moves vertically back and forth in the drawingand a speaker rim portion 68 which is mounted by conventional means to ahousing or cabinet 70. The vibrator arm, secured as by a suitable screwor other fastening mechanism 72 to the cabinet, or for that matterdirectly to the rim 68 of the speaker, extends downwardly (in thedrawing) generally parallel to the cone face and has a bent lowerportion, the vibrator impact end 74 which is adapted to be just abovethe voice coil 66 of the speaker. The voice coil 66 may be provided witha small contactor 76 which with the axial motion of the voice coil,tends to strike the impact end 74 of the vibrator arm 62. Each time thevibrator end 74, of a nonrigid type, is struck, the vibrator arm tendsto vibrate at its own resonant frequency, which may be selected to be ofa relatively high audio range, say in the order of 2 to 3 kilohertz. Thevibration of the vibrator arm tends to cause the cabinet 70 to resonatethereby amplifying the vibrational energy to produce an audio sound ofbuzz of increasing intensity as the signal to the voice coil increasesin intensity.

The vibrator arm 62 is provided with an adjusting screw 80 threadedthrough the vibrator arm. The screw 80 engages a shim 82 attached to thecabinet 70. By adjustment of the screw 80, the spacing'between thevibrator end 74 and the striker 76 may be varied. Thus as the spacing isadjusted the characteristic of the buzz or humming tone will be changedas is illustrated by the two characteristic lines 81 and 82 in the graphof FIG. 5. ln both cases, the vibrator signal starts at some finitelevel. This finite level is determined by the amplitude necessary forthe striker 76 to actually contact the vibrator end 74. Once contact ismade and the vibrator arm emits a very low-level buzzing signal, thissignal like that of the speaker generated signal, increases in intensityas the amplitude of the signal applied to the voice coil increases,until a maximum value is achieved. In general, smaller spacings of thevibrator end 74 from the contactor 76 provide louder audio intensities,i.e., the curve 81 represents the smaller spacing. The total audiooutput from the device of this invention is the sum of the two signals,i.e., tone from the loudspeaker plus the buzz of the vibrator arm.

The purpose of increasing the harmonic content of the power signal priorto application to the loudspeaker, or dual transducer 18, is to providea richer, more pleasing audible tone; to produce a signal containingfrequencies in the sensitive human hearing range where changes inintensity are the most easily discernible; and to permit the use of aconventional miniature permanent magnet dynamic loudspeaker, in anillustrative case, one having a 2-inch diameter cone.

Although such a small loudspeaker will not sufficiently radiate a 60 Hz.driving signal, the axial movement of its voice coil will follow the 60Hz. driving voltage. Therefore, a unique feature of this invention isthe use of the fundamental component of the 60 Hz. voltage to drive thevoice coil of said miniature loudspeaker through the mechanical motionsnecessary to actuate the vibrator (transducer No. 2). The 60 Hz. soundradiated by said miniature loudspeaker will be of relatively lowapparent intensity; while, simultaneously, harmonics produced by theharmonic generator undergo less attenuation by capacitor 42 than the 60Hz. fundamental frequency.

Loudspeakers of the electrodynamic-type are designed to normally operatewith cone amplitudes that fall within predetermined limits well withinthe low-impedance portion of their suspension means in order to transferelectric oscillatory energy to corresponding acoustical energy withreasonable high fidelity.

When the cone of the speaker is energized beyond the above mentionedrange, it gradually encounters increasing high-mechanical impedance ofthe suspension and thus requires a greater electrical energy input. Whenthis increased amplitude is suddenly arrested by impact with arelatively rigid body, the energy stored in the cone is released with anexcessive burst of acoustical energy which will produce complex shockwaves of sound with a considerably greater increase in sound energy ofshort duration, which waves are superposed on the normal acousticaloutput from the normal free cone output of the oscillatory signal.

Whereas a persons hearing is generally relatively insensitive to volumeor sound level changes at 60 Hz. because of loss of hearing efficiencyat that low frequency, it is well known that hearing efficiency andsensitivity to sound intensity changes increase with frequency until acertain upper frequency limit, varying with the individual, has beenreached, at which point efficiency and sensitivity again begin to taper.The

frequency of maximum sensitivity and efficiency also varies with theindividual.

Accordingly, an objective of the harmonic generator is to produceharmonics over such an audible frequency range that any person whosehearing is reasonably good, regardless of his frequency of maximumefficiency and sensitivity, will be able to hear the harmonic generatorproduced portion of the alarm signal throughout its low to high audiointensity range. Thus, this portion of the alarm system may be stated tobe individual to the users particular frequency of maximum sensitivityand efficiency.

In summary, a 60 Hz. fundamental voltage is'used to drive a miniatureloudspeaker voice coil so that the striker 76 will strike the buzzervibrator end 74 when the driving signal has reached a predeterminedlevel. With relatively low efficiency, a 60 Hz. sound is radiated by theloudspeaker cone. Simultaneously, harmonics of the 60 Hz. fundamentalfrequency are more efficiently radiated, giving tone richness to theloudspeaker output, and permitting the listener to hear distinct signalintensity changes ranging from nearly inaudible to a relativelyhigh-intensity level at which point the buzzer (transducer No. 2) isactivated. A dual signal results, consisting of the buzzer signal andthe harmonic generator signal, both increasing in intensity until theirrespective saturation or cutoff points have been reached.

The acoustical alarm device described has many advantages over those ofthe prior art. Due to the operation of the harmonic generator 16, thetone of the alarm device is far richer and more pleasing tothe car thanthat available from the ordinary alarrn. A major advantage lies in thedynamic range of the alarm system. When the system is turned on," thesignal reproduced by the loudspeaker is nearly inaudible, The outputsignal, complete with its harmonics, increases with time until a pointis reached at which the vibrator arm is also actuated to add amechanical buzz occurring at a separate and different frequency from thespeaker's audible signal, to the total audible signals from the device.When the vibrator first begins to operate, it produces a very low-levelsignal which builds to an output level or intensity equal to that of aconventional alarm clock. Thus, the alarm system begins operation with asingle, nearly inaudible, pleasing hum, and gradually advances itsoutput to a maximum which contains two basic signals: one from theloudspeaker emitting a 60 Hz. sound and strong amplified" harmonics anda second stronger signal from the buzzer, which produces a fundamentalfrequency (its actual resonant frequency) substantially higher than 60Hz. Typically, this buzz from the vibrator is a harsher signal and isutilized and operates only if the alarm is not disengaged prior to itsbeginning operation. This permits the light sleeper who is awakenedimmediately by the low intensity, rich tonal signal to shut off thealarm and thereby not be bothered by the harsher buzz. For the heaviersleeper, the operation by of the buzzer may be required before hisawaking. Thus, the alarm may be stated to be individual to the usersparticular threshold of sensitivity.

In an alternative embodiment of this invention, the vibrator mechanismillustrated in FIG. 3 may be modified to that illustrated in FIG. 4. Inthe illustration of FIG. 4, the same loudspeaker is illustrated ashaving the cone 64, rim portion 68 and voice coil 66 as previouslydescribed. In this instance, however, the vibrator arm 62 is attacheddirectly to the upper portion of the cone 64 as by a suitable adhesive.In this manner, the vibrator arm 62, which may be no more than a smallmetal strip, is energized by the vibratory mechanical energy of the coneto cause the free end 74 of the vibrator arm 62 to oscillate. Thus thevibrator end 74 engages the striker 76 of the voice coil. Since there isa phase difference between the voice coil vibrations and the vibrationsof the cone, several modes of vibrations are induced into the vibrator62 to produce a still different tonal quality.

It is now apparent that the oscillatory acoustical output of a flexiblediaphragm electromagnetic transducer which is rigidly secured to a frameabout the outer margin thereof and having a substantially rigid vibratormember positioned for oscillatory impingement at the center portion ofthe diaphragm will be responsive to a relatively high-input signal andwill produce high-energy audible shock waves considerably greater thanthat produced by the normal free operation of the cone, which mayinclude frequencies related to the resonant character of the vibratormember. The complex high-energy shock waves may also be superposed onthe predetermined relatively normal low oscillatory energy applied tothe diaphragm.

Whatever the particular loudspeaker-vibrator mechanism or other soundtransducer-vibrator mechanism employed, the invention provides arelatively simple transducer alarm.

It will be obvious that various modifications may be made in theapparatus and in the manner of operation it. It is intended to over suchmodifications and changes as would occur to those skilled in the art, asfar as the following claims permit and as far as consistent with thestate of the prior art.

What is claimed is: 1. An acoustic alarm device comprising incombination a sound transducing means,

switch means for applying a low-frequency alternating current voltagesignal to said sound transducing means thereby to produce an audiblesignal varying in content with the frequency and amplitude of saidvoltage signal,

impedance means coupled in circuit with said transducing means and saidswitch means for increasing as a function of time the amplitude of saidvoltage signal that is applied to said transducing means whereby theloudness of said audible signal progressively increases with time,

harmonic generating means coupled in circuit with said transducing meansfor generating harmonics of said voltage signal for application to saidtransducing means thereby producing an audible alarm signal improved intonal quality and containing frequencies in the sensitive human hearingrange where changes in alarm intensity are the most easily discernible,

a vibrator means adapted to be mechanically energized by said transducermeans thereby to produce a second audible signal.

2. An acoustic alarm device comprising in combination a soundtransducing means,

switch means for applying a low-frequency alternating current voltagesignal to said sound transducing means thereby to produce an audiblesignal varying in content with the frequency and amplitude of saidvoltage signal, impedance means coupled in circuit with said transducingmeans and said switch means for increasing as a function of time theamplitude of said voltage signal that is applied to said transducingmeans whereby the loudness of said audible signal progressivelyincreases with time, harmonic generating means coupled in circuit withsaid transducing means for generating harmonics of said voltage signalfor application to said transducing means thereby producing an audiblealarm signal improved in tonal quality and containing frequencies in thesensitive human hearing range where changes in alarm intensity are themost easily discernible, wherein said transducer means is a loudspeakerhaving a voice coil and a vibrator secured at one end to saidloudspeaker and adapted to be struck at the other end by the movement ofsaid voice coil thereby to produce vibratory energy in an audible range.

3. An acoustic alarm device comprising in combination a soundtransducing means,

switch means for applying a low-frequency alternating current voltagesignal to said sound transducing means thereby to produce an audiblesignal varying in content with the frequency and amplitude of saidvoltage signal, impedance means coupled in circuit with saidtransducingmeans and said switch means for increasing as a function of time theamplitude of said voltage signal that is applied audible signalprogressively increases with time,

are the most-easily discernible wherein'said transducer means is aloudspeaker having a voice coil and a vibrator secured to one end to thecone of saidloudspeaker whereby movement of said cone produces vibratoryenergy in said vibrator in an audible range.

1. An acoustic alarm device comprising in combination a soundtransducing means, switch means for applying a low-frequency alternatingcurrent voltage signal to said sound transducing means thereby toproduce an audible signal varying in content with the frequency andamplitude of said voltage signal, impedance means coupled in circuitwith said transducing means and said switch means for increasing as afunction of time the amplitude of said voltage signal that is applied tosaid transducing means whereby the loudness of said audible sigNalprogressively increases with time, harmonic generating means coupled incircuit with said transducing means for generating harmonics of saidvoltage signal for application to said transducing means therebyproducing an audible alarm signal improved in tonal quality andcontaining frequencies in the sensitive human hearing range wherechanges in alarm intensity are the most easily discernible, a vibratormeans adapted to be mechanically energized by said transducer meansthereby to produce a second audible signal.
 2. An acoustic alarm devicecomprising in combination a sound transducing means, switch means forapplying a low-frequency alternating current voltage signal to saidsound transducing means thereby to produce an audible signal varying incontent with the frequency and amplitude of said voltage signal,impedance means coupled in circuit with said transducing means and saidswitch means for increasing as a function of time the amplitude of saidvoltage signal that is applied to said transducing means whereby theloudness of said audible signal progressively increases with time,harmonic generating means coupled in circuit with said transducing meansfor generating harmonics of said voltage signal for application to saidtransducing means thereby producing an audible alarm signal improved intonal quality and containing frequencies in the sensitive human hearingrange where changes in alarm intensity are the most easily discernible,wherein said transducer means is a loudspeaker having a voice coil and avibrator secured at one end to said loudspeaker and adapted to be struckat the other end by the movement of said voice coil thereby to producevibratory energy in an audible range.
 3. An acoustic alarm devicecomprising in combination a sound transducing means, switch means forapplying a low-frequency alternating current voltage signal to saidsound transducing means thereby to produce an audible signal varying incontent with the frequency and amplitude of said voltage signal,impedance means coupled in circuit with said transducing means and saidswitch means for increasing as a function of time the amplitude of saidvoltage signal that is applied to said transducing means whereby theloudness of said audible signal progressively increases with time,harmonic generating means coupled in circuit with said transducing meansfor generating harmonics of said voltage signal for application to saidtransducing means thereby producing an audible alarm signal improved intonal quality and containing frequencies in the sensitive human hearingrange where changes in alarm intensity are the most easily discerniblewherein said transducer means is a loudspeaker having a voice coil and avibrator secured to one end to the cone of said loudspeaker wherebymovement of said cone produces vibratory energy in said vibrator in anaudible range.